This invention relates to pulse density modulation (PDM) microphone interface circuits, and, in particular, to low-power interface circuits for voice activity detection in mobile voice command applications.
Pulse-density modulation, or PDM, is a form of modulation used to represent an analog signal with a binary signal. In a PDM signal, the relative density of the pulses corresponds to the analog signal's amplitude. For example, a PDM encoding of an audio signal can be similar to the output of a 1-bit digital-to-analog converter (DAC). PDM encoding is often used in digital telephones.
Voice command applications in mobile devices are becoming more popular. The circuits that process audio signals detected by the microphone often consumes substantial power, because these circuits are typically always running as a voice command or keyword that can arrive at any time. For power efficient implementation and long battery life, it is desirable to have very low power circuits that process audio signals detected by the microphone.